user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/tests/rtld/rtld_next/libfoo.c

@@ -0,0 +1,17 @@
+#include <dlfcn.h>
+
+typedef char *charFn(void);
+
+__attribute__((weak))
+char *definedInBoth() {
+	return "foo";
+}
+
+charFn *fooGetDefault() {
+	return (charFn *)dlsym(RTLD_DEFAULT, "definedInBoth");
+}
+
+charFn *fooGetNext() {
+	return (charFn *)dlsym(RTLD_NEXT, "definedInBoth");
+}
+